JP4455725B2 - Method for correcting shape of quartz glass base material for optical fiber - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical fiber quartz glass base material (hereinafter simply referred to as a glass base material) used for manufacturing an optical communication fiber, and in particular, to a glass base material shape correcting method.
[0002]
[Prior art]
Non-circular shape is one of the structural characteristics of a glass base material composed of a transparent vitrified core and clad used in the manufacture of optical communication fibers.
This non-circular shape is expressed by a deviation from a perfect circle with respect to the outer peripheral shape of the glass base material, and can be expressed as a non-circularity Nc (%) as a parameter as follows.
Nc = (Dmax−Dmin) / D × 100 (%)
In the above equation, symbols Dmax, Dmin, and D are the maximum diameter (mm), minimum diameter (mm), and average diameter (mm) of the glass base material, respectively.
[0003]
In general, when the non-circularity Nc of the glass base material increases, the connection loss of the optical fiber obtained by drawing the glass base material increases. For this reason, conventionally, in a glass base material evaluation process, a glass base material having a non-circularity of a certain value (standard value) or more has been disposed of as a defective product.
[0004]
On the other hand, various shape correction methods have been considered in order to make a glass base material having a non-circularity Nc exceeding a standard value a non-defective product. For example, a method of mechanically polishing the periphery of a glass base material, or a method of chemically dissolving with an HF solution and etching is used.
However, although the method of mechanically polishing the periphery of the glass base material can remove minute projections on the surface, it is difficult to correct the peripheral shape to obtain a perfect circle. Also, in the method of chemically dissolving with HF solution and etching, simply by dipping in HF solution, the peripheral shape remains as it is evenly dissolved from the surface, and the non-circular shape is not changed. It is difficult to correct, and no correction technology has been established.
[0005]
[Problems to be solved by the invention]
An object of the present invention is to provide a glass base material shape correcting method for correcting a non-circular shape of a glass base material into a perfect circle.
[0006]
[Means for Solving the Problems]
To correct the non-circular shape of the glass base material, simply immersing the glass base material in the HF liquid simply turns the non-circular shape into a perfect circle shape by grinding uniformly in the radial direction of the glass base material. The effect is not recognized at all. Therefore, as a result of intensive studies on the state of the glass base material when the glass base material is immersed in the etching solution, the maximum diameter (Dmax) direction in the cross section perpendicular to the axis of the glass base material is on the etching liquid surface. The inventors have found that the non-circular shape of the glass base material can be corrected by immersing it in an etching solution up to the maximum radius so as to be perpendicular to the invention, and have completed the present invention.
[0007]
That is, in the glass base material shape correcting method according to claim 1, when the cross-sectional shape of the non-circular glass base material is corrected to a perfect circular shape using an etching solution, the glass held horizontally is maintained. The maximum diameter (Dmax) direction in the cross section perpendicular to the base metal axis is perpendicular to the etching liquid surface , and the maximum depth of water immersion is 0.5 times or less the maximum diameter (Dmax) of the glass base material. The non-circular shape of the glass base material is corrected by immersing the etchant in the etching solution from the lower surface side of the glass base material at a speed V and changing the speed V from the initial stage to the late stage of the non-circular correction. Yes.
Note that the rate V at which the glass base material is immersed in the etching solution is expressed as a function of the immersion depth L of the glass base material in the etching solution. That is,
V = {a (1 / D) ³ L ³ + b (1 / D) ² L ² + c (1 / D) L + d (1 / D)} Ve / Nc
(D: average outer diameter [mm] of glass base material, L: depth of immersion in etching solution [mm], Ve: etching rate [mm / min], Nc: non-circularity [%], a, b , C, d: constants).
[0008]
The glass base material shape correcting method according to claim 4, wherein the glass base material held horizontally when the cross-sectional shape of the non-circular glass base material is corrected to a perfect circular shape by using an etching solution. In the etching solution, the maximum diameter (Dmax) direction in the cross section perpendicular to the axis of the glass is perpendicular to the etching solution surface, and the maximum immersion depth is 0.5 times or less the maximum diameter (Dmax) of the glass base material. Non-circular shape of the glass base material is corrected by submerging the glass base material from the submerged state by lowering the etching liquid surface at a speed V ′ and changing the speed V ′ from the initial stage to the late stage of non-circular correction. It is characterized by doing.
The speed V ′ for lowering the etching liquid surface from the water immersion state is expressed as a function of the water immersion depth L of the glass base material in the etching liquid. That is, V ′ = {a (1 / D) ³ (Dmax / 2−L) ³ + b (1 / D) ² (Dmax / 2−L) ² + c (1 / D) (Dmax / 2−L ) + d (1 / D)} Ve / Nc
(D: average outer diameter [mm] of glass base material, L: depth of immersion in etching solution [mm], Ve: etching rate [mm / min], Nc: non-circularity [%], a, b , C, d: constants).
[0009]
To correct the non-circular shape of the glass base material, correct the glass base material by immersing it in the etchant from the lower surface side of the glass base material held horizontally, or by lowering the etchant surface from the submerged state. However, after correcting one maximum radius side of the glass base material with an etching solution, the glass base material is rotated by 180 ° around this axis to complete the other maximum radius side.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, the non-circular shape of the glass base material is corrected to a perfect circular shape by using an etching solution. As shown in FIGS. 1 (a), (b), and (c), the glass base material 1 The direction of the maximum diameter (Dmax) 2 in the cross section perpendicular to the axis is performed so as to be perpendicular to the etching liquid surface 3. Note that it is desirable to use an HF solution as the etching solution, and another acid or salt may be appropriately added thereto.
[0011]
To immerse the glass base material in the etchant, immerse the etchant in the etchant from the lower side of the horizontally held glass base material, or discharge the etchant out of the tank from the original submerged state. By doing so, the etching liquid level may be lowered.
For example, as shown in FIG. 1 (a), after the glass base material 1 held horizontally is placed in the etching treatment tank 5, the etching liquid 4 is supplied into the tank, and the liquid surface 3 The glass base material 1 is immersed in the etching liquid 4 from the lower surface side of the glass base material 1 or the glass base material 1 is lowered from above toward the etching liquid surface 3 as shown in FIG. The etching solution 4 may be immersed from the lower surface side of the material 1. Alternatively, as shown in FIG. 1 (c), the glass base material 1 may be lowered from the liquid level 3 to the liquid level 3 by discharging the etching solution 4 out of the bath from the submerged state. Reference numeral 6 denotes an installation base for the glass base material.
[0012]
In the correction, the maximum water immersion depth (Lmax) of the glass base material into the etching solution is set to the maximum radius, and one of the glass base materials is corrected by the etching solution and then rotated 180 ° around the axis. And correct the other largest radius side. At this time, the water immersion speeds V and V ′ of the glass base material are changed from the initial stage of the flooding to the latter half. In this way, the non-circular shape of the glass base material is corrected to a perfect circular shape.
[0013]
The water immersion speeds V and V ′ of the glass base material can be made a shape closer to a perfect circle by changing the speed from the initial stage to the latter half of the water immersion and correcting it based on the simulation and actual experimental results. In the modes (a) and (b), the initial water immersion speed V is slow, and the latter water immersion speed V is increased. In the embodiment of FIG. 1 (c), the initial flooding speed V ′ is fast and the latter flooding speed V ′ is slowed. These submergence speeds V and V ′ can be expressed by the above formula as a function of the depth L at which the glass base material is submerged in the etching solution, and the submergence depths V and V ′ are submerged in depth L. By controlling based on the above, the non-circular shape can be corrected to a perfect circle.
[0014]
【Example】
Hereinafter, one example of each of the examples and comparative examples of the present invention will be described, but the present invention is not limited to these examples, and various modes are possible within the scope of the claims.
Example 1
A glass base material having a non-circularity Nc of 1.0%, a maximum diameter of 50.250 mm, a minimum diameter of 49.750 mm, an average diameter of D 50.000 mm, and a length of 250 mm is placed in the HF liquid tank, and HF liquid is added from the bottom of the liquid tank. Supplied. Supply of the HF liquid was started, and the water immersion speed V of the glass base material after the glass base material began to be immersed in the HF liquid was controlled and changed by the following formula. The etching rate Ve at this time is 0.001667 mm / min.
V = {6330 (1 / 50.00) ³ L ³ -1720 (1 / 50.00) ² L ² + 235 (1 / 50.00) L + 50 (1 / 50.00)} × 0.001667 / 1.0
[0015]
The relationship between the liquid level rising speed (flooding speed) V and the flooding distance (flooding depth) L of the glass base material at this time is shown in FIG.
Here, the portion up to one maximum radius of the glass base material, that is, the maximum radius portion is corrected over 149 minutes, and then the glass base material is rotated 180 ° to correct the other maximum radius portion that is symmetric. As a result of further performing 149 minutes, the shape of the glass base material was corrected as follows.
The non-circularity Nc was 0.01%, the maximum diameter was 49.752 mm, the minimum diameter was 49.746 mm, and the average diameter was 49.750 mm.
[0016]
(Comparative Example 1)
A glass base material having a non-circularity Nc of 0.86%, a maximum diameter of 52.200 mm, a minimum diameter of 51.750 mm, an average diameter of D 51.975 mm, and a length of 250 mm is submerged in a liquid tank previously filled with HF liquid for 180 minutes. Etching was performed. The shape was as follows.
The non-circularity Nc was 0.87%, the maximum diameter was 51.600 mm, the minimum diameter was 51.150 mm, and the average diameter was D51.375 mm.
[0017]
【The invention's effect】
According to the present invention, correction of a non-circular shape that has been difficult with a conventional method of immersing in an etching solution is facilitated, and a glass base material having a large non-circularity that has been discarded as a defective structure can be regenerated. Productivity, and productivity can be greatly improved.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a schematic explanatory view for explaining a method for immersing an etchant in accordance with the present invention, wherein FIGS.
FIG. 2 is a graph showing the relationship between the water immersion speed V (liquid level rising speed) and the water immersion depth L (water immersion distance) of the glass base material in an example of the present invention.
[Explanation of symbols]
1 Glass base material 2 Maximum diameter (Dmax)
3, 3 Liquid level 4 Etching solution 5 Etching tank 6 Glass base

Claims (7)

When the cross-sectional shape of the glass base material having a non-circular shape is corrected to a perfect circular shape using an etching solution, the maximum diameter (Dmax) direction in the cross-section perpendicular to the axis of the glass base material held horizontally is In order to be perpendicular to the etching liquid surface and the maximum water immersion depth is 0.5 times or less the maximum diameter (Dmax) of the glass base material, the etching liquid is submerged at a speed V from the lower surface side of the glass base material, A method for correcting a shape of a quartz glass preform for optical fibers, wherein the velocity V is changed from the initial stage to the later stage of correcting the non-circular shape, thereby correcting the non-circular shape of the glass preform. The method for correcting a shape of a quartz glass preform for an optical fiber according to claim 1 , wherein the rate V at which the glass preform is immersed in the etching solution is expressed as a function of the immersion depth L of the glass preform in the etching solution. The function has the following expression V = {a (1 / D ) 3 L 3 + b (1 / D) 2 L 2 + c (1 / D) L + d (1 / D)} Ve / Nc
(D: average outer diameter [mm] of glass base material, L: depth of immersion in etching solution [mm], Ve: etching rate [mm / min], Nc: non-circularity [%], a, b , C, d: constant) The method for correcting the shape of a quartz glass preform for optical fiber according to claim 2 . When the cross-sectional shape of the glass base material having a non-circular shape is corrected to a perfect circular shape using an etching solution, the maximum diameter (Dmax) direction in the cross-section perpendicular to the axis of the glass base material held horizontally is The etching liquid surface is immersed in the etching liquid so that it is perpendicular to the etching liquid surface and the maximum water immersion depth is 0.5 times or less of the maximum diameter (Dmax) of the glass base material. The shape of the quartz glass base material for optical fiber, wherein the non-circular shape of the glass base material is corrected by lowering at a speed V ′ and changing the speed V ′ from the initial stage to the late stage of the non-circular shape correction. How to fix. The quartz glass preform for an optical fiber according to claim 4 , wherein the rate V 'of lowering the etching solution surface from the water immersion state is expressed as a function of the water immersion depth L of the glass substrate in the etching solution. Shape correction method. The function is expressed by the following formula: V ′ = {a (1 / D) ³ (Dmax / 2−L) ³ + b (1 / D) ² (Dmax / 2−L) ² + c (1 / D) (Dmax / 2−L) + d (1 / D)} Ve / Nc
(D: average outer diameter [mm] of glass base material, L: depth of immersion in etching solution [mm], Ve: etching rate [mm / min], Nc: non-circularity [%], a, b , C, d: constants) The method for correcting the shape of the quartz glass preform for optical fiber according to claim 5 . After modifying one maximum radius side of the glass base material which is horizontally held in an etching solution of claim 1 to 6 said glass base material by 180 ° rotation to the axis to correct the other maximum radius side A method for correcting the shape of a quartz glass preform for an optical fiber according to any one of the above.

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